what is the alternative for Services.AddMvc() and SuperJsonOutputFormatter used in .Net Core 2.2 while migrating to .Net Core 3.1

Question

I'm migrating a .Net Core 2.2 web API application having API Controllers only with no views. I have a custom API response set in my project using SuperJsonOutputFormatter. Now, I'm using NewtonsoftJsonOutputFormatter for creating custom response for the APIs. But as per microsoft document services.AddMvc() is obsolete in .Net Core 3.1. So, how to call the customformatter in startup.cs. I'm using the below code

services.AddControllers().AddNewtonsoftJson(options =>
{
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
    options.SerializerSettings.Formatting = Formatting.Indented;
});
services.AddScoped<SuperJsonOutputFormatterFilter>();
services.AddMvc(opts =>
{
    opts.EnableEndpointRouting = false;
    var oldFormatter = opts.OutputFormatters.OfType<CustomOutputFormatter>().Single();
    opts.OutputFormatters.Remove(oldFormatter);
    var replacementJsonOutputFormatter =
       new CustomOutputFormatter(oldFormatter.serializerSettings, ArrayPool<char>.Shared);
    opts.OutputFormatters.Add(replacementJsonOutputFormatter);
}).SetCompatibilityVersion(CompatibilityVersion.Version_3_0);

The configure services is as below

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
   if (env.IsDevelopment())
   {
      app.UseDeveloperExceptionPage();
   }
   else
   {
      app.UseHsts();
   }
   app.UseRouting();
   app.UseExceptionHandler("/Error");
   app.UseAuthentication();
   app.UseStaticFiles();
   app.UseHttpsRedirection();
   app.UseMvc();
}

The above code gives a runtime error that Some services are not able to be constructed, Error while validating the service descriptor. How to call customformatter without using Services.AppMvc()

My Error_Helper is as below

ErrorDescription Class

 public class ErrorDescription
    {
        public ErrorDescription(HttpStatusCode statusCode)
        {
            this.Code = (int)statusCode;
            this.Description = GetDescription((int)statusCode);
        }

        string GetDescription(int statusCode)
        {
            return statusCode switch
            {
                404 => "Employee ID not found",
                500 => "Internal server error",
                400 => "Device token already registered",
                406 => "No data found in table",
                _ => "",
            };
        }


        [JsonProperty("errorCode")]
        public int Code { get; set; }
        [JsonProperty("errorDescription")]
        public string Description { get; set; }
    }

FormatterFilter Class

 public class CustomJsonOutputFormatterFilter : IAsyncActionFilter
    {
        private readonly CustomOutputFormatter _formatter;
        // inject SuperJsonOutputFormatter service
        public CustomJsonOutputFormatterFilter(CustomOutputFormatter formatter)
        {
            this._formatter = formatter;
        }
        // a helper method that provides an ObjectResult wrapper over the raw object
        private ObjectResult WrapObjectResult(ActionExecutedContext context, object obj)
        {
            var wrapper = new ObjectResult(obj);
            wrapper.Formatters.Add(this._formatter);
            context.Result = wrapper;
            return wrapper;
        }

        public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
        {
            ActionExecutedContext resultContext = await next();
            // in case we get a 500
            if (resultContext.Exception != null && !resultContext.ExceptionHandled)
            {
                var ewrapper = this.WrapObjectResult(resultContext, new { });
                ewrapper.StatusCode = (int)HttpStatusCode.InternalServerError;
                resultContext.ExceptionHandled = true;
                return;
            }
            else
            {
                switch (resultContext.Result)
                {
                    case BadRequestObjectResult b:      // 400 with an object
                        var bwrapper = this.WrapObjectResult(resultContext, b.Value);
                        bwrapper.StatusCode = b.StatusCode;
                        break;
                    case NotFoundObjectResult n:        // 404 with an object
                        var nwrapper = this.WrapObjectResult(resultContext, n.Value);
                        nwrapper.StatusCode = n.StatusCode;
                        break;
                    case ObjectResult o:                // plain object
                        this.WrapObjectResult(resultContext, o.Value);
                        break;
                    case JsonResult j:                  // plain json
                        this.WrapObjectResult(resultContext, j.Value);
                        break;
                    case StatusCodeResult s:             // other statusCodeResult(including NotFound,NoContent,...), you might want to custom this case 
                        var swrapper = this.WrapObjectResult(resultContext, new { result="" });
                        swrapper.StatusCode = s.StatusCode;
                        break;
                }
            }
        }

    }

Custom Outputformatter Class, this class calls the customformatterfilter

 public class CustomOutputFormatter : NewtonsoftJsonOutputFormatter
    {
        public CustomOutputFormatter(JsonSerializerSettings serializerSettings,
            ArrayPool<char> charPool) : base (serializerSettings, charPool)
        {
        }

        public JsonSerializerSettings serializerSettings { get; private set; }



        public override async Task WriteResponseBodyAsync(
            OutputFormatterWriteContext context,
            Encoding selectedEncoding)
        {

            if (context == null)
                throw new ArgumentNullException(nameof(context));
            if (selectedEncoding == null)
            if (selectedEncoding == null)
                throw new ArgumentNullException(nameof(selectedEncoding));
            using TextWriter writer = context.WriterFactory(context.HttpContext.Response.Body, selectedEncoding);
            var statusCode = context.HttpContext.Response.StatusCode;
            var rewrittenValue = new
            {
                status = IsSucceeded(statusCode),
                error = IsSucceeded(statusCode) ? null : new ErrorDescription((HttpStatusCode)statusCode),
                data = context.Object,
            };
            writer.Write(rewrittenValue);
            this.CreateJsonWriter(writer);
            await writer.FlushAsync();

        }

        private bool IsSucceeded(int statusCode)
        {
            // 204 is not an error but handled
            if (statusCode >= 400 || statusCode == 204) { return false; }
            return true;
        }
    }

Answer 1

I haven't looked in detail at your implementation (it seems quite convoluted, what are you trying to achieve?), but you can use UseControllers() in the same way as you were using UseMvc() previously to configure the MvcOptions instance. e.g:

services.AddControllers(options =>
{
    options.InputFormatters.Insert(0, new VcardInputFormatter());
    options.OutputFormatters.Insert(0, new VcardOutputFormatter());
})

That might solve your problem - there's no need to call AddMvc.

However, the error "Some services are not able to be constructed" suggests you are missing a service dependency. The error message will tell you which one. This is a new feature in .NET Core 3.1, service provider validation, that you can read about in this blog post.